I think I may have figured it out, it seems as though the sheets  which throw
up the error have a space in the footer. The only clue I had was that (none)
was not displayed in the custom footer when looking at the sheet.

So, how to code around that? If there is a space or multiple spaces, I want
t replace the text with my text. However, if there is actually text in the
footer, then I want to append my footer to the existing footer.